Why are High Pressure Systems So Much Larger Than Low Pressure Systems?

[Coach McGuirk]

That is my question. I've never seen a small but extreme high pressure system unlike with low pressure systems.

[WestWind]

Since no one has answered this yet I will make an attempt. I am not a meteorologist - weather is a hobby for me. So others with more knowledge, please correct anything I state incorrectly.

It has to do with centrifugal force.

As the winds increase around a strengthening low, centrifugal force pushes air outward away from the low. Thus the stronger the winds, the more centrifugal force, and the stronger the pressure gradient becomes. The only limiting factor as to how high the winds can become is the amount of energy available to the low. Strong winds imply a tight pressure gradient. A tight pressure gradient means the pressure increases rapidly when moving away from the center of the low. Thus lows are relatively small.

As the winds attempt to increase around a strengthening high, centrifugal force pushes air outward away from the high. This lowers the pressure in the center of the high, and thus the high weakens. The only way a high can maintain itself is to have light winds. Light winds imply a weak pressure gradient. A weak pressure gradient means the pressure decreases only slowly when moving away from the center of the high. Thus highs are relatively large.

The equations involved are discussed in this book (Chapter 9 under the topic Gradient Wind):

http://www.amazon.co...s and engineers

[Amped]

In a high pressure winds tend to flow outward due to friction. In a low pressure they tend to flow inward. This allows high pressures to expand. The pressures and forces section of this site has pictures to explain most of it.

http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/bndy.rxml

http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/grad.rxml

[famartin]

I believe the reason is due to the forcing mechanism/location.  High pressure is caused mainly due to confluence in the upper troposphere, while low pressure can be caused by either difluence in the upper troposphere or by strong lift in the lower troposphere (often associated with convective bouyancy).  Because low pressure can be forced in the lower troposphere where mesoscale forces can dominate, you can get small but intense low pressure systems.  Meanwhile, highs are forced mainly in the upper troposphere where mesoscale processes essentially don't exist. 

 

I hope that's right, I'm not good at answering questions.  There's probably more to it.